A HVDC power distribution network or a HVDC power transmission system uses direct current for the transmission of electrical power, in contrast to the more common AC systems. For long-distance transmission or distribution, HVDC systems may be less expensive and may suffer lower electrical losses. In general, a HVDC power transmission system comprises at least one long-distance HVDC link or cable for carrying direct current a long distance, e.g. under sea, and converter stations for converting alternating current to direct current for input to the HVDC power transmission system and converter stations for converting direct current back to alternating current.
U.S. Pat. No. 6,788,033 and U.S. Pat. No. 5,734,258 disclose DC to DC conversion and relate to stationary or portable systems powered by a DC battery, and to electric vehicles. U.S. Pat. No. 6,914,420 describes a power converter for converting power between a first and a second voltage, and relates to electric vehicles.
U.S. Pat. No. 7,518,266 discloses an AC power transmission system, where a DC transmission ring is used, utilizing controllable AC-DC converters in a multi-in-feed/out-feed arrangement.
U.S. Pat. No. 3,694,728 describes a HVDC mesh-operated network comprising several interconnected stations for effecting an exchange of power by means of converters located at the stations and which are connected to AC networks.
DE 2530789 discloses an arrangement for protecting a converter connected to a DC line, the arrangement comprising a surge arrester connected in series with a non-linear resistor.
U.S. Pat. No. 3,694,728 describes a circuit arrangement for altering current distribution in mesh-operated HVDC transmission networks.
JP2000-175361 discloses an alternating current direct current hybrid power transmission system.
WO 2007/022744 describes a current-limiting switch, which may be connected to a DC network, including a mechanical switching unit, a power-electronic switching unit, a capacitive short-circuit limitation unit and a varistor.
WO 2011/095624 discloses a circuit for connecting and disconnecting an energizable electric system and an electric network of a vehicle, the circuit comprising a mechanical circuit breaker and a semiconductor switch.
WO 2011/124258 describes a power electronic converter for use in HVDC power transmission.
DE 1513827 discloses an apparatus for influencing the current distribution in a HVDC network.